This invention relates generally to fuel injection limiting maps, and more particularly to a system and method for adjusting an application of a fuel injection limiting map to compensate for injector variability.
The performance of individual fuel injectors in a fuel injection system may vary from one another as well as from that of a nominal fuel injector. A nominal fuel injector dispenses a known quantity of fuel for a fixed on time, but real injectors may dispense a different quantity of fuel for the fixed on time. The variability of real fuel injectors results at least in part from machining tolerances in the manufacture of the multiple components that make up a complete fuel injector. Each fuel injector is preferably tested following manufacture, and rejected if the performance of the injector diverges from that of a nominal injector by a predetermined magnitude. Performance of acceptable fuel injectors, however, may still vary from performance of a nominal injector. As a result, real fuel injectors may, for example, dispense too little fuel at a short on time but too much at a long on time. The variability of an actual fuel injector may be exacerbated through use as well, resulting in altered behavior over time.
Systems and methods are known to correct for variability of fuel injectors in a fuel injection system. One such method is taught by Thomas in U.S. Pat. No. 5,839,420, entitled System and Method of Compensating for Injector Variability and issued on Nov. 24, 1998. This method or system determines an appropriate calibration code for each injector based on the performance difference of the injector compared to a nominal fuel injector. A logic controller uses this calibration code to alter on times determined by the engine control unit, thus causing the injector to perform more like a nominal injector and a group of injectors to perform more uniformly.
Another method is disclosed in U.S. Pat. No. 5,634,448 to Shinogle et al. entitled Method and Structure for Controlling an Apparatus, such as a Fuel Injector, Using Electronic Trimming and issued on Jun. 3, 1997. This method reduces the effects of variability introduced by the manufacturing and assembly process of an apparatus, such as a fuel injector or other fuel system component, by adjusting a base fuel delivery signal for each injector. After applying what is usually a unique adjustment to each injector, they perform more uniformly.
The electronic control module of a fuel injection system references fuel quantity limiting maps stored in memory to decrease the amount of fuel dispensed by an injector under certain conditions. One such limiting map, a smoke map limit, is based on the maximum allowable fuel that should be delivered into the cylinder given the amount of air available. For example, the injection of fuel into the cylinders of the engine during acceleration may be excessive, resulting in excess smoke. Another type of limiting map, the torque map limit, is based on the maximum allowable fuel delivered into the cylinder given the physical limitations of components of the engine. For example, excessive torque can result in damage to the engine. Methods are also known for adjusting fuel map limits to improve performance and emissions such as that taught by Barnes in U.S. Pat. No. 5,586,538 entitled Method of Correcting Engine Maps Based on Engine Temperature and issued on Dec. 24, 1996. This method modifies at least one of the fuel map limits, such as the smoke map limit or torque map limit, in response to engine temperature, thus ensuring that the fuel injectors dispense a desired amount of fuel.
The uniform application of fuel map limits, however, fails to account for injector variability. As a result, injectors that dispense too little fuel at a particular on time due to variability are unduly limited. Similarly, injectors that dispense too much fuel at a particular on time due to variability are not limited enough.
The present invention is directed to overcoming one or more of the problems as set forth above and to overcoming other problems associated with uniform application of fuel quantity limiting maps.
In one aspect of the present invention, a method of adjusting an application of a fuel injection limiting map is disclosed. A performance difference between at least one fuel injector and a like number of nominal fuel injectors is estimated. If the performance difference exceeds a predetermined value, the application of one or more various fuel limiting maps is adjusted.
In another aspect of the present invention, a fuel injection system has a plurality of fuel injectors in communication with an electronic control module to control their operation. The fuel injection system has a means for adjusting a limiting map if a performance difference between the injector and a like number of nominal injectors exceeds a predetermined value.
In still another aspect of the present invention, a method of reducing smoke emissions from an engine having an electronically controlled fuel injection system is disclosed. An electronic control module with a nominal smoke limiting map is provided. If the fuel injection system performance deviates from a nominal system performance by a predetermined value, the application of the smoke limiting map is adjusted.